The four common sizes of hearing aid batteries from smallest to largest are: 10 (yellow tab), 312 (brown tab), 13 (orange tab), and 675 (blue tab). The smallest battery will last between 3-6 days while the largest will last a little longer than 2 weeks.
All hearing aid batteries have little holes on the positive (flat) side. When you remove the battery from the package, oxygen enters the holes and activates the battery. Don’t remove the battery from the package, or protective backing, until you are ready to use it. Also, be sure to give a new battery a couple of minutes to activate completely before you put it in your hearing aid.
Virtually all hearing aids have a battery door that is designed to help you properly insert the battery. Sometimes there is a little picture on the door itself. Other times, the door has a little shelf that will guide you. In virtually every instance, the battery door will not shut properly if the battery is upside down. Finally, all hearing aids on the market today use the door as a receptacle for the battery; never try to insert the battery into the hearing aid.